The JHAVÉ Project

• JHAVÉ: Java Hosted Algorithm Visualization Environment

• Goal: Development of a comprehensive suite of visualization-based materials for teaching algorithms and data structures, work was partially supported by a National Science Foundation Grant, CCLI-EMD #0126494

• Principal Investigators:• Scott Grissom (Grand Valley State University)• Myles McNally (Alma College)• Thomas Naps (University of Wisconsin - Oshkosh)

• Website: http://jhave.org

JHAVÉ “supports” Effective AV -- How?

• “Stop-and-think” questions• Documentation window• Pseudo-code window• Input generators• Audio accompaniment

A Tour of the JHAVÉ Website

JHAVÉ Organization

• Client-server mode of operation• Generation of visualization script occurs by running

algorithm on server• Viewing of script handled by “dumb” rendering

client• Webstart facilitates deployment

• Users just need to access the appropriate website to run the client on their machine

• JHAVÉ supports a variety of scripting languages through plug-ins

The JHAVÉ Client-Server Model

Algorithm Choice

Input Generator Presented

Script is Rendered

Appropriate Input Generator Served

Appropriate Script Generation

Program Run

Client ServerData Flows

Choice

InputGenerator

Input

Vis Script

Overall GAIGS VIS Script Structure

• A GAIGS visualization script is defined in a show file

• The general script structure is:• one or more snapshots• followed by an optional question collection

• The show file could be created by hand, or (more usually) as the output of a script generating program

Example of Overall Script Structure

<show>

<snap> … </snap>

<snap> … </snap>

<snap> … </snap>

<questions> … </questions>

</show>

A Show File with Three Snapshots and a Question Collection

A Simple, but Complete, Example<?xml version="1.0" encoding="UTF-8"?><!DOCTYPE show PUBLIC "-//JHAVE//DTD GAIGS SHO//EN" "gaigs_sho.dtd">

<show><snap>

<title>queue</title><pseudocode_url>index.php?line=2</pseudocode_url><queue>

<list_item color="#0000FF"><label>9</label>

</list_item></queue><question_ref ref="0"/>

</snap><questions>

<question type="MCQUESTION" id="0"><question_text>Color of the next queue item?</question_text><answer_option>red</answer_option><answer_option is_correct="yes">green</answer_option><answer_option>blue</answer_option>

</question></questions>

</show>A Simple Visualization Script with a Multiple Choice Question

Generating Scripts

• GAIGS XML scripts can be generated by programs written in any programming language

• However, the JHAVÉ environment is designed to directly support programs written in Java

• Input to programs must be specified on the command line

• The first command line parameter is the file name the script is to be written to

• Support classes are available which can be used to directly generate the required GAIGS XML

Support Classes for Script Generation

• ShowFile: Handles the actual writing to the script file• Structure Classes: Basically one for each of the

GAIGS built-in structures• Linear Structures: GAIGSstack, GAIGSqueue,

GAIGSlist• Arrays: GAIGSarray (includes bar graphs)• Trees and Graphs: GAIGStree, GAIGSgraph• Text: GAIGStext

• Question Classes: Support various aspects of generating questions in scripts

• XMLfibQuestion, XMLmcQuestion, XMLmsQuestion, XMLtfQuestion

The ShowFile Class

• The ShowFile class is responsible for all writing to the script file

• Constructors:• ShowFile(String fileName)

• file is opened, and preliminary XML written to it• Key Methods:

• writeSnap(String title, Double titleSize, GAIGSdatastr… ds)

• writes to the file the XML for a snap with the title and each of the listed structures

• close()• writes any questions and closes the file

The GAIGSstack Class I

• GAIGSstack functions in the usual way as a stack (with push and pop operations

• But also stores color and other information in a way that can remain hidden (if desired) from the client class

• Constructors:• GAIGSstack()

• create a stack using defaults for location and color• GAIGSstack(String n, String c, double x1, y1, x2, y2,

size)• create a stack with name n, color c, location

<(x1,y1),(y2,y2)>, and fontSize size

The GAIGSstack Class II

• Key Methods:• pop()• push(Object o)• push(Object o, String c)

• Key Inherited Methods (from GAIGSlist)• isEmpty()• peek()

import exe.*;import java.io.*;

public class Example1 {static final String title = "Stack Example";static final double titleSize = 0.08;

public static void main (String [] args) throws IOException {

GAIGSstack stack = new GAIGSstack();

ShowFile show = new ShowFile(args[0]);int itemsToAdd = Integer.parseInt(args[1]);

for (int i = 0; i < itemsToAdd; i++) {

stack.push(i);show.writeSnap(title, titleSize, stack);

}show.close();

}}

Example Code: Using the ShowFile and GAIGSstack Classes

<?xml version="1.0" encoding="UTF-8"?><!DOCTYPE show PUBLIC "-//JHAVE//DTD GAIGS SHO//EN"

"gaigs_sho.dtd">

<show>

<snap><title>Stack Example</title><stack><bounds x1="0.0" y1="0.0" x2="1.0" y2="1.0" fontsize="0.05"/><list_item color="#FFFFFF"><label>0</label></list_item></stack></snap>

<questions></questions></show>

Example Output: itemsToAdd == 1

ShowFile constructor

ShowFile writeSnap

ShowFile close

GAIGSarray I

• GAIGS provides support for one and two dimensional arrays

• Row labels can be specified, and if the array is 2-d column labels as well

• If the array is a 1-d array of int, it can be shown either in the usual format or as a bar graph

• Here we just briefly consider the 1-d case, please consult the GAIGS API for complete details on this class

GAIGSarray II

• Constructor:

• GAIGSarray (String s, boolean bar, color c, double x1, y1, x2, y2, size)

• create a label with name s, color c, location <(x1,y1),(y2,y2)>, and fontSize size. Display as a bargraph if bar == true

GAIGSarray III

• Key Methods:• set(Object o, int loc) and set(Object o, int loc,

String c)• set location loc to have value o, optionally with

color c• get(int loc)

• return the value at location loc• setColor(int loc, String c)

• set the color of the item at location loc to c• setName(String s)

• set the name of this structure to s

Activity: Bubblesort Visualization

• Our exercise will be to create a complete visualization for the (infamous) Bubblesort algorithm

• Supplied code will create the snapshot shown below:

Supplied Code

import java.io.*;import java.util.Random;import exe.*;

public class Sort {

static final String TITLE = null; // no titlestatic int arraySize; // # of items to sortstatic GAIGSarray items; // the array of items

Exercise Code: Preamble

public static void main(String args[]) throws IOException {

// process program parameters and create the show file objectShowFile show = new ShowFile(args[0]);arraySize = Integer.parseInt(args[1]);

// define the two structures in the show snapshotsitems = new GAIGSarray(arraySize, true, "BubbleSort",

"#999999", 0.1, 0.1, 0.9, 0.9, 0.07);

// initialize the array to be sorted & show itloadArray(); show.writeSnap(TITLE, items);

for (int pass = 1; pass < arraySize; pass++)

for (int i = 0; i < arraySize-pass; i++)if ((Integer)(items.get(i)) > (Integer)(items.get(i+1)))

swap(i, i+1);

// visualization is doneshow.close();

}

Exercise Code: Main method

// Load the array with values from 1 to the array size, then// shuffle these values so that they appear in random order.

private static void loadArray () {Random rand = new Random();for (int i = 0; i < arraySize; i++)

items.set(i+1,i);for (int i = 0; i < arraySize-1; i++)

swap(i, i + (Math.abs(rand.nextInt()) % (arraySize - i)) );

}

// Swap two items in the array. private static void swap (int loc1, int loc2) {

Object temp = items.get(loc1);items.set(items.get(loc2), loc1);items.set(temp, loc2);

}

Exercise Code: Support Routines

If you decide to do the activity …

1. Decide when snapshots should be taken (when do the interesting events occur?)

2. Use coloring to show the ongoing actions of the algorithm

3. Use the name of the array to produce useful messages about the status of the algorithm

Adding Interactive Questions

• GAIGS Scripts can be used to ask four types of

questions:

• True / False

• Fill in the Blank

• Multiple Choice

• Multiple SelectionA Multiple Choice Question

Question Basics

• All the questions in a GAIGS script are collected at the end of the XML File

• Each contains a unique ID number/identifier

• A snapshot can contain a question reference• The reference is by ID number/identifier• A question reference causes the question to

appear when the snapshot is shown

Question Generation Support I

• As for GAIGS structures, there are support classes for the generation of question XML

• XMLtfQuestion: true / false• XMLmcQuestion: multiple choice• XMLmsQuestion: multiple selection• XMLfibQuestion: fill in the blank

• Each support class allows the definition of the question text, choices, and correct answer(s)

Question Generation Support II

• To include a question in a snap, pass a question in ShowFile method writeSnap

• This method also require documentation and pseudocode urls (which may be null)

• writeSnap(String title, double titleSize, String doc_url, String pseudo_url, question q, GAIGSdatastr… ds)

• writes to the file the XML for a snap with the title, titleSize, documentation and pseudocode urls, a question and each of the listed data structures

XMLtfQuestion

• Constructor:• XMLtfQuestion(ShowFile f, String id)

• The id string must be unique within a script• ShowFile reference is a legacy code issue

• Key Methods: • setQuestionText(String text)

• sets the text which will be displayed as the question

• setAnswer(boolean value)• set the correct answer to value

XMLtfQuestion Example

int id = 0;boolean swapIsDone = false;

…

XMLtfQuestion tf = new XMLtfQuestion(show, id + "");id++;tf.setQuestionText("Will a swap be done next?");

…

show.writeSnap(TITLE, null, null, tf, …);

…

tf.setAnswer(swapIsDone);

XMLfibQuestion

• Constructor:• XMLfibQuestion(ShowFile f, String id)

• The id string must be unique within a script• ShowFile reference is a legacy code issue

• Key Methods: • setQuestionText(String text)

• sets the text which will be displayed as the question

• setAnswer(String text)• set text to be one of answers to be accepted as

correct

XMLfibQuestion Example

int id = 0;int swapsThisPass = 0;

…

XMLfibQuestion fib = new XMLfibQuestion(show, id + "");id++;fib.setQuestionText("How many swaps will be made this pass?");

…

show.writeSnap(TITLE, null, null, fib, …);

…

fib.setAnswer(swapsThisPass + "");

Probabilistic Question Asking

• The support classes allow the user to define the number of questions to be asked during a session, despite how many are “added”

• To do this, use the alternative constructor for ShowFile:

• ShowFile(String fileName, int count)

• Exactly count questions will be asked (as long as at least that many questions have been added)

Next Activity: Bubblesort + Questions

Return to your Bubblesort visualization and

1. Add a question which asks how many swaps will be made during the next pass (asked just before a pass)

2. Add a question which asks if a swap will be made (asked just before a comparison is made)

3. Use probabilistic questioning to limit the number of questions asked during a session